This invention relates to apparatus for sealing a clearance between two components in relative movement with respect to one another, where a sealing strip is arranged between the two components in a direction transverse to the direction of movement to bear against a sealing face of the first component to seal the clearance. Apparatus of this general description has been disclosed in British Patent Document GB 2 078 306.
Reliable sealing of hot gas and/or pressure energized clearances formed between adjacent components poses substantial problems especially when the components are moving relative to one another, as is the case with exhaust gas nozzles of turbojet engines or rocket propulsion systems. Thus, plane nozzle walls and flaps as they are used on variable 2D nozzles are exposed to differential, thermally induced expansions resulting from the jet of hot exhaust gas. This problem has been tackled in the above-noted GB 2 078 306 A, where a cylindrical seal is arranged in the clearance between two surfaces facing one another at an angle. For this purpose, the seal is retained on the face of a first surface and urged under the action of a leaf spring against the second surface for sealing effect. At the elevated temperatures prevailing in the exhaust gas stream of exhaust nozzles, springs prove to be insufficiently reliable. Another consideration is that it is impossible to flexibly adapt the spring to varying operating conditions, since on account of the spring characteristic, a defined contact pressure can be set at a single operating point only.
In a broad aspect of the present invention, apparatus of the above generic description is provided to operate reliably and with little wear also under pressure and at elevated temperatures, with operationally caused component movements being duly considered.
It is a particular object of the present invention to provide an arrangement where the sealing strip is allowed to float in a groove in the second component on a fluid flowing all around between the groove and the sealing strip and is urged by the fluid against the first component, where the fluid is channeled into the groove through feed ducts in the second component, and where the operating pressure of the fluid exceeds the ambient pressure surrounding the components.
The means of the present invention advantageously provides a reliably operating seal to protect against the ingress especially of pressurized hot gas. The fluid used to position the seal simultaneously provides the necessary contact pressure of the sealing strip against the first component and protects the sealing strip from direct exposure to hot gas. No-contact positioning of the sealing element within the groove of the second component ensures low-wear and, hence, trouble-free operation of the sealing means. The sealing action of the fluid stream permits the contact pressure of the sealing element against the first component to be reduced. This in turn reduces the actuating forces required for displacing the components relative to one another, as perhaps in nozzle actuation.
Controlling the volume and/or pressure of the gas stream permits the apparatus to be flexibly adapted to varying operating conditions also on short call. With the gas temperature and feed flow selected to suit, the gas stream will have a cooling effect on adjacent components.
Temperature and pressure induced distortions of the components are advantageously balanced automatically by causing the fluid to consistently urge the sealing strip into the clearance at a nearly constant pressure. In a preferred aspect of the present invention the second component is provided with cooling ducts, as it will be necessary with thermally highly-stressed variable nozzle flaps on exhaust gas nozzles, and the cooling ducts are connected to the feed ducts to permit the passage of fluid. Interconnecting the ducts in this manner ensures the supply of fluid to the sealing apparatus while eliminating the need for additional inlet lines from a fluid source. Simultaneously, effective cooling of the sealing strip can be achieved.
In an advantageous aspect of the present invention the groove takes the shape of a V-slot, making the groove easy to manufacture. For this purpose, the sealing strip is given a triangular section.
In an alternative arrangement the sealing strip is given a rectangular section, which permits the automatic balancing of expansion movements of the components relative to one another without causing the size of fluid clearance between the legs of the groove and the sealing strip to change. This eliminates the risk of adversely affecting the flow by expansion movements. In a further preferred aspect of the present invention the sealing strip is given a rectangular section with a round projection. This reduces the risk of canting when the components are moving.
A sealing strip optimized to reduce the canting risk is provided by an embodiment of the invention which has a circular section shaped sealing strip. Additionally, the actuating forces needed to displace the components can then be reduced, the round sealing strip being able to travel across the sealing face through rolling motion.
To reduce also the actuating forces of sealing strips with an abutting lateral surface, these strips are designed in accordance with certain preferred embodiments with relief grooves. Pressurizing the relief grooves with fluid under operating pressure causes a force component to counter the contact pressure of the sealing strip and so reduces the actuating force required to move the components.
In certain preferred embodiments, the sealing strip is segmented to ensure it conforms to the sealing surface when in contact with it. The sealing integrity of the sealing apparatus is therefore ensured also when the sealing face should warp.
To give the sealing apparatus greater thermal stability and reduce thermal expansions when the components are exposed to high-temperature gases, preferred embodiments include cooling grooves.
In certain preferred embodiments, seal cooling ducts or grooves are tapped at a compressor of a gas turbine engine in connecting lines and the components are a lateral wall and a variable nozzle flap of an exhaust gas nozzle. The use of this arrangement on turbojet engines provides special advantages in that the contact pressure of the sealing strip against the lateral wall of an exhaust gas nozzle is made a function of engine load, the pressure being supplied by air tapped at the turbojet engine's compressor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic longitudinal sectional view illustrating a turbojet engine with variable exhaust gas nozzle, constructed according to a preferred embodiment of the invention;
FIG. 2 is a sectional view illustrating a portion of a first nozzle flap embodiment with rectangular sealing strip usable in the arrangement of FIG. 1;
FIG. 3 is a sectional view illustrating a portion of a second nozzle flap embodiment with triangular sealing strip usable in the arrangement of FIG. 1;
FIG. 4 is a sectional view illustrating a portion of a third nozzle flap embodiment with circular sealing strip usable in the arrangement of FIG. 1;
FIG. 5 is a sectional view illustrating a portion of a fourth nozzle flap embodiment with rectangular sealing strip and round projection usable in the arrangement of FIG. 1; and
FIG. 6 is a partial perspective view illustrating a portion of a fifth nozzle flap embodiment with a rectangular sealing strip usable in the arrangement of FIG. 1.